Field of the Invention:
The invention relates to a pressure transducer, in particular for sensing a lateral collision in a motor vehicle, which converts a pressure signal into an electric useful signal that is determined by an output signal of a variable-sensitivity sensor device, in which the sensor device and a control device form a single-loop control loop, and in which a control difference of the control device is determined by a setpoint and the output signal of the sensor device.
A pressure transducer which is known from International Publication WO 94/11223 uses an air pressure detector as a sensor to monitor the air pressure in a cavity of a motor vehicle side part, in particular in the event of a lateral collision of the motor vehicle, and emits an electric useful signal which is determined by the measured air pressure change. An electronic system evaluates the useful signal and, if appropriate, triggers restraining devices of the motor vehicle.
The useful signal of such a pressure transducer is not unambiguous.
U.S. Pat. No. 3,717,038 discloses a pressure transducer for determining the gas flow in a gas-operated engine. The pressure transducer has two sensor devices. The first sensor device picks up a pressure change in a measuring pipe and the second sensor device picks up the ambient pressure. The second sensor device is disposed in a feedback line of a control loop, with a control device which has a proportional behavior, as does the controlled system. A differential amplifier forms a control difference from output signals of the two sensor devices. An output signal of the differential amplifier is fed as a controlled variable to the second sensor device and influences the sensitivity of the second sensor device. The pressure transducer delivers a signal, at the output of the comparator, which is proportional to the pressure change in relation to the ambient pressure.
Such a pressure transducer requires two sensor devices which measure different pressure variables independently of each other. However, neither of the two sensor devices picks up the total pressure as the sum of the ambient pressure and a pressure change.
In U.S. Pat. No. 3,841,150, a pressure transducer is proposed in which an output signal of a sensor device depends on pressure changes. The sensor device contains two piezo-resistive measuring resistors on a diaphragm. A constant-current circuit configuration with a voltage source, operational amplifiers and calibration resistors ensures a constant current flow through the measuring resistors. The voltage difference between the voltages across the measuring resistors on one hand is used as a useful signal and on the other hand is fed back to the constant-current circuit configuration, in order to increase the linearity of the sensor device.